In the conventional color monitors or color picture receiver, detecting signals for the automatic white balance detection are used for automatic white balance adjustment circuits which automatically adjust the white balance or semiautomatic white balance adjustment circuits requiring a preset. Such automatic white balance detection signals follow vertical blanking signals. FIG. 2 is a connection diagram of a basic structure of the automatic white balance circuits which use the automatic white balance detection signals. FIG. 3 is a view illustrative of signal wave-forms of the automatic white balance detecting signals.
In FIG. 2, a circuit block 10 comprises circuits for generating the automatic white balance detection signals and picture driver circuits. The circuit block 10 at its input side receives vertical blanking pulses and image signals and is connected to an output side of an error amplifier 16. The circuit block 10 at its output side is connected to a base of an image output transistor 18. The image output transistor 18 is connected at its collector side through a pull-up resistance 20 to a positive power supply +E, in addition through a diode 22 to a cathode of the CRT. The image output transistor 18 is grounded at its emitter side through a resistance 26. The diode 22 is connected at its anode and cathode sides to a p-n-p transistor 28 at its base and emitter respectively. The p-n-p transistor 28 is connected at its collector to sample-hold circuits 30 and is grounded through a resistance 32. The sample-hold circuits 30 are connected at its output side to a positive input terminal of the error amplifier 16. A negative input terminal of the error amplifier 16 is grounded through a reference power supply 34.
The conventional automatic white balance circuits so constructed are operated as follows. Normally, as shown in FIG. 3, the automatic white balance detection signals synchronize with horizontal signals and indicate a white level voltage. Such automatic white balance detection signals are inserted during n interval 2H immediately after the vertical blanking signal in which H is the interval between starting times of a scanning line and a next scanning line. A current being proportional to a cathode current I.sub.K of the CRT flows through the p-n-p transistor 28 to the resistance 32 so that a voltage V.sub.RS is generated at the resistance 32. A voltage value of a part of the voltage corresponding to the automatic white balance detection signals is subjected to the sample-hold by a sampling pulse V.sub.P of the sample hold circuits 30 and inputted into a positive input terminal of the error amplifier 16 having at its one output side the reference voltage supply 34. The error amplifier 16 makes a feed-back of the difference of the inputted voltage by the sample hold circuits 30 from the reference voltage V.sub.r to the circuit block 10. The circuit block 10 controls a base voltage of an image output transistor 18 so as to change a collector voltage V.sub.c of the image output transistor 18. As a result, automatic balance circuits are so operated as to keep the cathode current I.sub.K of the CRT constant.
However, according to the above automatic balance circuits, when a normal vertical deflection circuit is used as a vertical deflection circuit which generates vertical blanking pulses 12 to be inputted to the circuit block 10, there exists the following problem. In the normal TV broadcast picture receiver, the over-scanning so appears that the scanning lines are largely deflected in the vertical and horizontal directions from the CRT screen. As a result, when the normal vertical deflection circuit is used to make the deflection, the automatic white balance detection signals inserted immediately after the vertical blanking pulses appears outside the screen and thus dose not appear on the screen. In such a case, there exists no problem. However, in a CRT of a color monitor such as a medical display monitor, there exists a problem in that detection signals clearly appear on an upper portion of the screen as white lines.
It is such reason that although the scanning lines of the color monitors are deflected so as to appear small inside the CRT screen, for example, 99% thereby resulting in the under-scanning. This is undesirable for the screen performance.
Accordingly, it is an object of the present invention to provide a vertical deflection circuit capable of producing a normal screen in which the automatic white balance detection signals inserted to make the automatic white balance adjustment do not appear on the screen.
It is a further object of the present invention to provide a vertical deflection circuit having a freely adjustable detecting signal deflection position, which remains within the CRT as to minimize a secondary reflection of electron beams, if any.